Deviation correction for cathoderay beams



Pam 4, E949. Y A. c. MUNSTER,

DEVIATION CORRECTION FOR GATHODE-RAY BEAMS Filed Nov. 25, 194e I 2 Sheets-Sheet l AGI/V75 Jan. 4, B949., A. c. MUNSTER 2,457,911

I l DEVIATION CORRENTI'ION.FOR CATHODEPRY BEAMS Filed Nov. 25, 1946 A i 2 sheets-sheet :a

INVENTOR. Auf/v c fafa/wmf Pat'ented Jan. 4?, l1949 UNIT DEVIi-TIN CRRECTIN- FOR'CATHGDE- RAY BEAMS fllen C.l\/Iunster. Philadelphia, Pa., assigner to Philco Corporation, Philadelphia, Pa., a` corporation of Pennsylvania Application November 23, 1946,:Serial No. 711;,969i

8 Claims. l

The invention described and claimed herein relates to control means for cathode ray tubes. More particularly, the invention provides automatic control means for correcting, substantially instantaneously, an unintended deviation in a controllable physical feature of an electron beam, as for example, an unintended deviation in the position of the beam.

The present invention` is of particular utility in television systems Where it may beconveniently employed to correct an undesired departure of the spot of the scanning electron beam. from a preselected path the beam is intended tofollow. Control of this nature is particularly desirable in multi-color television systems employing a cathode-ray tube having a multi-color striped or mosaic-line screen, or in three-dimensional television systems employing a cathode-ray tube having differently polarized screen elements in striped arrangement, since deviation of the scanning spot from its intended scanning path introduces error in the picture being viewed which may be noticeable and objectionable.

In black; and white television systems employing a conventional scanning pattern comprised of a plurality of vertically-displaced parallel lateral lines, the beam spot ofthe viewing tube may deviate vertically from its scanning path a limited amount without the effect of.` such deviation being noticeable to the observer. But in multi-color or stereoscopic television systems employing striped' screens, considerably less vertical deviation is permissible before the verror i's noticeable. In short, for good quality of reproduction in these types of color and three-dimensional television systems, it is important that the spot of the scanning beam adhere closely to the line it is intended to scan. Apparatus which may be satisfactory for controlling the scanning of a black and white television tube, may not be at all satisfactory for controlling the scanning of a multi-color or polarized television tube, because of the more rigid requirements of color and three-dimensional presentation,

The instant invention provides an additional beam which functions as the control' means, and this control beam is effective in one embodiment of the invention, to maintain the spot of the electron scanning beam accurately positioned as the said spot moves along a predetermined path despite undesired and unavoidable fluctuations in tube potentials which tend to displace the spot therefrom.

An important advantageof the present invention is that the control beam is free of lany i 2 intensity-modulating signals which are applied to the beam which is to be controlled, as for ex-- ample, the scanning beam ofthe cameraor:` The control system isV thereforey viewing tubes. continuously eective irrespective of Whether-or not the scanning beam of the camera. or viewing tube is intensity modulated to zero, or.- to a very. low` value.

It is an object of this invention to provide a secondV beam of electried particles as a control. means for correcting, substantially instantaneous- 1y, unwanted deviations of afirstbeam. of. electried particles from. al predetermined desired condition with respect to. a controllable physicalv feature thereof, as for example, with respect to its instantaneous. position.

It is another object of this invention to provide a control' beam for maintaining rthe scanning beam of a cathode-ray tube accurately positioned upon a` predetermined path.

It is a further object o'f this invention to `provide a control beam which is effective to maintain the intensity-modulated scanning Abeam of a cathode ray tube accurately positioned upon. a predetermined scanning path irrespective of the instantaneous intensity of the modulated beam.

It is another object of. this'inventionv to provide control means capable of correcting, substantially instantaneously, undesired vertical deviations of a scanning beam from a substantially 'horizontal scanning pattern; and asa more specific object, capable of functioning in' three-color television systems employing an every-thirdeline interlace scanning pattern.

These and other objects and features of' the presentinvention will be clear from a consideration of the following detailed description taken. in conjunction with the accompanying drawings in which:

Figurev lis', an illustration, partly schematic, partly diagrammatic, of a circuit embodying one form of the invention;

vFigure 2 is a diagrammatic representation of one arrangement of control-tube screen target which may beV employed with the system illustrated in Figure l Figure 3 isa diagrammatic representation of an alternatev arrangement of control-tube screenk target which `may be employed with every-otherlin-e interlace scanning; and

Figure ll is a schematic representation of a spiral-scanI control target.

Referring now to Figure 1, thereis illustrated a cathode ray tube 'IU having electron beam `IIf impingent upon screen I2. The scanning. ac-

curacy of beam Il is controlled by the novel means of the present invention and tube lil is therefore indicated in Figure 1 as being the controlled tube. Controlled tube i@ may serve as the picture tube of e. television receiver, or as the camera tube of a television transmitter, or may serve other cathode ray tube functions.

For the purpose of facilitating the description of the present invention, tube I will be assumed to be the picture tube of a three-color television receiver, having a screen I2 comprised of luminescent material arranged in closely spaced, substantially horizontal, parallel lines. Adjacent lines will be assumed to be comprised of different luminescent material, as for example, a different phosphor; and every third line will be assumed to be comprised of the same phosphor. Or, alternatively, screen I2 may be comprised of a common fluorescent material, as for example, a `white phosphor, to one surface of which color lter material has been applied in closely-spaced, narrow, lateral strips or lines, adjacent strips being different color filters and every third strip being the same color lter.

v In Figure 1 of the drawing, only nine horizontal line positions of screen I2 are shown. These are identified by the reference letters a. to i inclusive, andr they are intended to be illustrative of the much larger number of lines of which the screen of an actual three-color television picture tube is 9 comprised.

In accordance with the present invention, a second screen and a second beam are provided which function to assure accuracy of scanning on the part of beam II of tube lil. The second screen and second beam are preferably contained in a separate envelope; and accordingly there is shown, in Figure l, an auxiliary tube I3 containing the second screen and beam to which reference has just been made. Tube I3 will be referredto as the control tube, and it may, with the exception of screen I4, be of conventional construction. In the particular embodiment now being described, screen I4 is comprised of a plurality of narrow, closely spaced, mutually insulated, substantially horizontal, parallel strips of conductive material, which may, but need not, be luminescent. These conductive Strips function as the target plates for beam I5 of the control tube. For each line of mosaic-line screen I2 there is a corresponding target strip on screen Ill; and for reasons that will become clear, an eXtra strip is preferably added at the top and bottom of the target screen. In the embodiment being described, controltube beam I5 is deiiected both vertically and horizontally in such manner that its scanning pattern is similar to, and preferably identical with, that of beam II. If the horizontal deflections of beams II and I5 be identical, then the lengths of the target strips may of course, be equal to the lengths of the lines of screen I2. If the horizontal deflection of control beam I5 be smaller or larger than that of beam II, then the target strips may be shorter or longer than the lines of screen I2; but the time required for the control beam to complete one lateral sweep, should be equal to the time required for beam II to scan one line. And of cours-e the vertical deflections of both beams should be equal, or at least proportional, during the scanning of a line.

Referring now to Figure 2, there is illustrated schematically the physical arrangement and the electrical connections of the target strips of screen I4 as employed in the embodiment of my invention now being described. Only eleven target strips, a to z", inclusive, aa. and ii', are shown, but these are intended to be representative of the large number of target strips of which the screen of tube I3 will ordinarily be comprised, the actual number of strips being preferably larger by two than the number of lines in the picture tube. Nine of the strips shown, i. e. strips a to c" inclusive, correspond to the nine lines, a. to z' inclusive, of fluorescent screen I2 which are shown in Figure 1. The other two strips, aa and iz", are extra target strips, one being provided at the top of the screen and the other at the bottom of the screen. The target strips are shown as having a slight downward slope to the right, which corresponds with the scanning lines of fluorescent screen I2, it being understood that the customary scanning action is from left to right across the image and downward.

Every third target strip of screen I4 is electrically connected to a common lead, thus forming tlree groups of interlaced target elements. In Figures 1 and 2 of the drawings, a group comprising strips a', d', g and iz" are shown connected to common lead R, a second group comprising strips b', e and h are shown connected to common lead B; and a third group comprising strips aa', c', f and z" are shown connected to common lead Gr. The target strips connected to lead R may be deemed to -correspond to lines of screen I2 comprised of a luminescent phosphor which under electron bombardment emits a red color. Similarly, the target strips connected to leads B and G may be considered as corresponding to lines of screen I2 comprised of blue and green phosphor respectively.

Referring again to Figure 1, a suitable positive potential is applied to each of the target strips by way of the common leads R, B, G, and resistors 2'I, 28, 29, respectively. Capacitor 3U is a by-pass capacitor. Each of the three common leads, R, B and G, is connected to suitable switching means I5 through which control signals are passed to feedback connections I9 and 2B. The control signals referred to are derived from the impingement of electrons of beam I5 upon one of the conductive target strips. For as the impinging electrons return to cathode 4I through one of the resistors 2l, 28, 29, a signal is developed at the ungrounded end of the resistor, which is available for control purposes.

In order to effectuate the desired control, the switching means provided in the present illustration are adapted to accomplish the following: (a) provide an open circuit between each of the feedback connections I9, 2B and the target strip corresponding to the line intended to be scanned; (b) provide a closed circuit between one feedback connection and the target strip corresponding to the line adjacent and above the line intended to be scanned; (c) provide a closed circuit between the other feedback connection and the target strip corresponding to the line adjacent and below the line intended to be scanned.

The switching means for accomplishing the above may be of any suitable form, preferably electronic. However, for the purpose of describing the instant embodiment, it will suilice to illustrate and describe a mechanical switching arrangement. There is accordingly shown in Figure l, a pair of rotary-type switches I 'I and I 8, having rotatable switch arms 25, 26 respectively and each having three arcuate contact-segments L, M, N and L', M', N respectively. Each of the aimais@ threer'co'mmon leads R, Bf. and G, is:connectedto; one of the three segmentsofeachswitch; In-the illustration, lead B isy connected; .to segments..M andMf, leadR is connectedzto segments Il. and L', andl'eadlG is connectedtolsegmentsN aindNr'-,

Switch armsz, 26 are gangedftogether and are output of amplifier 22 is shown applied to a phase inverter 23, but if desired, the inversion of the signal may of course be accomplished by having ampliiier 22 comprise less, stage than ampliiier zI. The output signals of amplifier EI and the inverted signals of amplier 22 are combinedin voltage adder 24 and are applied by way of common connection 34 and switch S to voltage adder 35 where they are combined with the vertical deflection signals from source 35;

If' desired, the control signals fed back by wayl ofv connections I9 and 28 may be applied respecttively to opposing elements of the Vertical deiiecting means in which case inversion of the signals oi'one of the paths is unnecessary.

Referring again to cathode ray tubes l0 and I3, it has been indicated previously that these tubes, with the exception of screen I4, may be of conventional construction; therefore, tube elements andv associated circuits, which are conventional and well known are merely shown inblock forms.

Tube Ii! is shown in the drawing as having a cathode 3l, a signal grid 38, horizontal deflecting means indicated by block 39, and vertical deflecting means indicated'by block d'0. Control tube I3 is shown as having cathode 4I, a signal grid 42, horizontal deflecting means indicated by block 3, and vertical deflecting means indicated by block 44.

Vertical deection signals from source 36 are applied by way of voltage adder 35 and amplifier 5to Vertical deflection means 40 of tube I0 and areV applied simultaneously to vertical deecting means-44 of tube I3,

Horizontal deflection signals from source 46 are applied through amplifier il to. horizontal deecting means 330i tube Ill and, in the preferred embodiment now being described, are simultaneously applied to the horizontal deflecting means i3 of control tube I3. In some embodiments of my invention, as is described later in the speciiication, the horizontal deecting signals are not applied to the control tube, the control beam being deflectedvertically only.

Picture and blanking signals, as from source 58, are applied to control grid 38 of tube I0, while blanking signals only are applied to control grid d'2? of control tube I3 since beam I5 is preferably not intensity modulated. If desired, the application of blanking signals to grid 42 ofrtube I3 mayv also be omitted, but if this be done, a gating tube isinserted in the control-signal feedback connection 34, arranged to bar the feedback of control signals produced during retrace periods.

The operation of -the instant embodiment oflmy novel circuit will now be described. As indicated above, Vertical deiiection signal'sfrom vsource 36- one more, or onev ar'eizapplied: simultaneously to vertical deiiectingl means 40 of tubeliand-Miofi tube I3 tofthefendf that electron beams Il 4and I5.- are moved in'. a similar vertical, manner. Horizontal deiiection. signals -frorn source A6, are'appliedisimultaneouslyl to horizon-tal?deectionmeans t9-and t3vto=move beams LI? and |15, throughl similar, horizont-a1 scanning .paths:. Other potentialsviniiuencing de-v ilectiontas-for'example, the Aquadag potentials (not, shownareV likewise applied. to both tubes fromfcommonisourcesa.

Assume an instant in the scanning pattern` when beamz I tof'- picture tulbe wis scanning a,

blue: phosphor line, as forexample line b. Atg that same instant, coordinated beam, t5; of control tubeY lf3 isiocusedupon targetv strip'b'. Tan--` get-stripe b Iis connected tocommon lead B, and` lead- B. is connected to segment M of switch1 lflfand; segmentMof; switch i8: Assume further that an unavoidable-fluctuation occurs in one-orv more-of the potentials affecting vertical defiec tiontcausingv beams H: and I5 to deviate.- inva downward direction `from their proper' positiona In so deviating, some or. all of the electronswk of' controlfbeam I5 strike target strip` c and aavoltagefis developedacross resistor-29A whose maghi tude is a function, of, the number of electrons-f which impinge upon strip c'. As statedfaboven beam l5: is notv intensity modulated` with: pic',-4 ture signals; and the vintensity offy the `beamg. and the size of thebeam: spot, during. thev scanfning periods are predetermined: and` iixedl Consequently; the voltage producedv across resistor 2'9: by the impingement. of; electrons upon target strip: c" is' also` predetermined' and fixed, exceptfor the factv that the downward deviation; of'beam I5 may beso vsmall that only the lower.1

portion ofthe beam spot encounters target-strip;

c' in which, casega smaller voltage is developed.

Incidentally, the size'-l of the spot of beam i5? mayA preferably beA suchy that when the beam `isA centered upon, for: example strip b, the peripher-y of'. the spot just escapes contact with adjacent. strips. a' and c.

Returning now to the example being described; in which a downward deviation has just occurred causingelectrons to strike target strip c', it will: be vseenV that'strip'c is connected to commoirl'ea-d G, .and-leadGJisf connected'to'segment N of.Y switch; I'IY and-N-' 'ofTk switch: |18. YRotating switch arm 2li.x of switch I1 is in Contact with segment N, and the voltage produced across resistor 29' is applied byway of connection IS tothe input circuit of.` amplifier 2-I'. The voltage ydeveloped across thel output circuitV ofv ampliiier 2SIV is applied by way ofY leadI 35i to voltage adder 35 where it is com'- bined with the' vertical deflecting signals fromsource 315i The polarity and magnitude of the' voltage delivered by amplifier 2l is such that it is'effective' to movev beams I'I and I5 in an upward` direction, preferably to such an extent thatA target strip b. is overshot and a portion of the electrons strike target stripa! which is `adjacent and.

above.

It. will benoticed that` when control beam I5 deviateddownwardly from strip b toc', no correction-signalfwas obtained vfrom amplifier 221for. the'reasonthat connection 2'!! was open, at switch` I'8, .switch` arm `2'5 being out of. contact with seg-I ment' N.

It should'A vbe mentioned.' here that the irequency" response` characteristics` of ampliiier 121i and '22. are preferably such that steep wavefront control signals may bepassed therethrough, 'thus termining vertical deflection. When anupwardk deviation from line positions b, b occurs, electrons from beam I strike target strip a', which is connected to common lead R, lead kR being connected to segment L of switch I1 and segt ment L' of switch I3. Switch arm 25 of switch Il is not in contact with segment L, and feedback connection l 9 is consequently open at switch I7. Switch arm 26 of switch I8 is, however, in contact with segment L', and the voltage produced across resistor 2l as ar result of electrons striking target strip a is therefore applied across the input circuit of amplierZZ. For input signals of like polarity, the output signals of ampli# er 22 are either of opposite polarity from those of amplier ZI, or if of the same polarity are inverted in phase inverter 23; and the signal is then applied to voltage adder 35 by way of connection 34. The effect of combining the signals from amplifier 22 with the vertical deflection signals from source 35 is to move beams II and I5 in a downward direction, preferably to such an eX- tent that strip b is overshot and aportionof the electrons strike target strip c.

It will be observed thatnwhen line positions b, b are being properly scanned, the voltage developed across resistor 28, as a result of electrons impinging upon target strip b, is not applied to voltage adder 35 for the reason that both the feedback circuits I9 and 2U are open at segments M and M of switches I'I and I8 respectively.

It will be seen that in the embodiment just described, the control or correcting voltages are applied at the slightest deviation of the controlbeam spot from its proper position. And if overshooting control voltages are employed, as by suitable adjustment of the gain and time-delay introduced by amplifiers 2l, 22, then the beam, following an unwanted departure, is given an oscillatory motion whose frequency is preferably higher than that of the picture elements, and amplifiers 2l and 22 are peaked ampliers adapted to pass the oscillatory frequency, as well as lower frequencies.

In order to effectuate the desired switching, switch aims 25, 26 are rotated in coordination with the movement of scanning beams II' and I5, the rotating speed of the switch arms being dependent upon the scanning pattern being employed. In a three-color system employing a multi-color mosaic-line screen, an every-thirdline interlaced scanning pattern may be conveniently employed. With such a scanning pattern, switch arms 25 and 26 of switches I'I and I8 are rotated clockise, and are so timed as to remain in engagement with each switch segment during the scanning of a field, i. e. during the scanning of the lines common to a single color. For example, arm 25 engages segmenty N and. arm 26 engages segment L at the instant that @beams li and l5 start to sweep line positions b, b respectively. Beams II and I5 complete scanning of the color iield of which line b is a component, at the same instant that rotating arms 25, 25 complete their respective passages over switch segments N and L. During the period required for beams II and I5 to return. to line positions c, c' at the top of the screen,

switch arms 25, 26 traverse the spaces between switch'segments N, L and L', M.r

As beams II and I5 scan the next color field, the uppermost line positions of which are c, c respectively, the arrangement shown in Figure 1 continues to be effective to provide vertical deflection control similar to that just described in connection with the preceding field. This may f be readily conrmed by an examination of the circuit arrangement of Figure 1, and a detailed description thereof is not believed to be necessary.

The control system illustrated in Figure 1 and described above, is also applicable to television systems employing everyotherline interlaced scanning or yevery--liney sequential scanning. Where everyother-line interlaced scanning is to be used with the arrangement illustrated in Fign ure 1, every third target strip may be connected to a common lead, just as in the case of everythird-line interlace scanning, but if this be done switch elements' 25, y2li should be rotated counter-clockwise instead yof clockwise, and the speed of rotation should be such thatk elements 25, 25 sweep over a switchr segment during the time required to scan a single line position. This requires a very high rotary speed, well beyond the capabilities of most mechanical switches, but well within the capabilities of an electronic switching device, as for example, a radial-beam tube. The switchingfarrangement shown schematically in Figure 1 and thus far referred to in mechanical terms, may be deemed to be also a schematic representation of a radial-beam tube in which elements L, M, N and L', M', N, represent separate anodes arranged in circular fashion about cathodes 3l, 3'2, and in which rotating ele-y ments 25 and 26 represent beams of electrons which are rotated about the axes of the tubes in known manner, as by the application of a rotating magnetic and/or electric fields.

Assume the system to be as described in the above paragraph, i. e., having an every-otherline interlaced scanning pattern and radial-beam tube switches, the beams of which rotate counterclockwise at a speed of one anode for each line-scan, with element 26 lagging element 25 by one anode as shown in Figure 1. The angular positions occupied by elements 25, 26 in the drawing assume that line b, or a line of the same field as line b, is being scanned. It may be readily seen from an examination of the circuit of Figure 1, that at all times during the scanning cycle, the voltage developed across the resistor corresponding to the line intended to be scanned, is not fed back to the voltage adder 35 because of the fact that both circuits are open at the switches. However, for a downward deviation, it will be seen that a correcting signal is fed back by way of connection I9 and amplifier 2l, while for an upward deviation, a correctingsignal of opposite polarity is fed back by way of connection 20, amplier 22 and phase inverter 23..

If the target-strip pattern and switching ar rangement shown. in Figure l be employed when the scanning pattern requires that every line be scanned in sequence, then radial-beam tubes are preferably employed as switches, and the beams represented by switch elements 25, 26, should be rotated clockwise at a speed of one anode for each line scanned, with element 25 lagging element 26 by one anode. Ii this be done, then control is obtained in a manner similar to that described above for every-third-line and everyother-line scanning.

*It is tto .be :understood that .my inventionv :is .not limited .to ithe fspecic .fpattern o interlaced target strips illustrated kin :Figures 1 and 2. Other 'target strip varrangements imay `of course beused. Eorexamplawhere an every-'other-line v,interlaced .scanning fpattern :is to 4be employed, screen lili :of :control tube i3 @may .conveniently take the form shown iin 4Figure-.3.

`In Figure.Bionlytwotarget strip vnetworks are employed Sand. these are so :positioned 'that the target strips fcorrespcnd -to the vspaces between .the mosaic AlinesA-ofjgaicture `tube 'I'.ll. 'Where the arrangement of Figure 13 .is lused, Ythe'operation is as follows: Assume line "position `cazof tube :Nl is beingscanned. vThefspotlof coordinatedrbeam |5 lis then `positioned in the space yab, .located between target .strips au and bb, and vvthe spot follows the path 'indicated "bythe dotted line. If desired, .the spotfmayfbe Vof.suchs'izethat some of the electrons impingc upon target strip am,

and :a substantially fequ'al :number :upon strip ibb, in which case control nvoltagesof 'equal vamltop 'posite :polarity are .ted back, .and t-iare effective to. maintain .the beam :spot 'substantially :centered intthe space ab. .Following thefsc'annin'g 'of `line `0L ofitube `I U,line.c.is1next scanned, during .which time the spot of beam :l5 .occupies fthe spacev cd between targetlst'rips .cc 'and-dd. Upon complet- 4ing the scanningof .a1eldc'omprised of alter- .nate lines, beams vl-l andlfreturn to 'thetop of ythe screen; .line .b lis vthen scanned .and `the Acontrol-'beam spotzmoves along space `bc .located Tbetween .target strips fb'b andre.

`With .the arrangement of IFigure i3, switching "is onlynecessary at the 'end-of leach iield; hence z'.

a pair of .twosegment rotary 'type mechanical switches, 51552, drivenv at y a 'speed of `one :revolution Iper frame, will be satisfactory.

With respect now to ltl'leifnatter of d'eecting -controlbeam t5 inra horizontal-direction-as well as :in .a vvertical vdirection,?I have assumed in the preferred embodiments -'described above, both horizontal =and .verticaldeecti'on signals 'to be appliedltofcontrol-be'am 15.. If this be done, and if 'the deflection characteristics of Itubes fill' and I5-s be falike, lcontrol 'beam L15' .moves 1in an iden- 'tical .manner .with fthat i-of 'beam H. 'In `some lcases, it may v:be preferable, 3as for purposes 'of vincreasing'the accuracy-of thefcon'trol, to fuse' a controltube whi'chi'sfof largerfsize than the picfture 'or Acamera ltube which is to fbe controlled; and in that case control beam FIS maytbe'lmoved -over fa similar but lproportionatelylarger scan- Inin'g .pattern than -be'arn il I'.

If ldesired, the horzontal"deection vof Acontrol :beam it' may be shortened, or 'even eliminated altogether, "as by 'means tof switch H. In the flatter case, 'attention lis Sdrawn tothe fact that :if the lines to bescanned `have a slightvdowniward slope, as Ais ordinarily :the case, then the end tof :a line just scanned imay be at a lower .level 'than `the .beginning foi one vor more 4lines lznextsadiacenti'below. In the case offevery-thirdilin'e interlaced scanning, ffor example, "the -end of a line :which 4has just been scanned is probably Yat fa lower 'level 'than the beginning foi the next two `lines immediately' therebeneath. It -will tl'ierefm'ev -be .seen that, if 'the control beam `is deflected 'vertically only, zits 'normal downward .movement during the Ascanning oi 'a line would, ,in certain scanning patterns, bring .the 'control beam across ilevels'corresponding to portions of @ne .or more lines 'next :ad-jacent lloelow the :line being scanned. :In: such '.cases,l .itis zdesirableto feliminate the. usual. .downwardr'slope 7'ci the scan- 10 ning line and to maintain the scanning lines absolutely horizontal. This may be accomplished by-means of the control voltages. It will be understood from whathas been said previously that the control voltages developed by the impingement of control-beam electrons upon a target strip are variable to thel extent that the voltages developed increase in magnitude as the encroachment of the control-beam spot upon the target strip increases. Hence, in order to prevent the scanning beam from taking its usual downward course as it moves from lleft to right across the image, the control system may be-so adjusted that as the control voltages increase in magnitude they'compensate for the-linear change occurring in the vertical deiiection `potentials during the scanning of a line. At the lend of each linee scan, the control signals -are blanked out, whereupon the scanning and control beams, during retrace, abruptly drop through one or two line positions to take up `the proper positions for scanning the lnext line of the pattern.

`It is also to be understood that my -control system is not limited to scanning patterns in which the lines to `be scanned are horizontal, or substantially horizontal, i. e. having the customaryslight downward slope. On the contrary, my system will operate quite satisfactorily with scanning patterns of various configurations as, for exampleywith a spiral scanning pattern. As

will be understood by'those skilled vinthe art, a yspiral scanning pattern maybe obtained by amplitude-modulating horizontal' and'vertical deiiec- 4tion signals which are sinusoidal andr90out of phase.

If it be yassumed Athat the horizontal deflection signals providedbyisource @E :of Figure 1 are'90 out of phase with the verticaldeilection signals provided vby source "3i, and that both be sinusoidal, then the modulation vnecessary -or lspiral scanning may be Iprovided by a saw-tooth voltage *from generator 511 by :way of switch lW and `voltage adder 3 to yvertical and horizontal `amplifiers `l5 and M, so as =to control the gain thereof.

The control voltages fed back vby ivvay of lead 34 may then'be applied byway ofswitch 'S to voltage adder d8 to control Athe accuracy 'of the radial deflection.

For the control of'spiral scanning, two target strips of spiral vconfiguration may be employed, as is illustrated in Figure'l. The space between the strips defines the path-the beam is intended to follow. If the beam deviates outwardly, `electrons impingey upontarget'stripr, 'and the voltage `developedy across resistor 49 is fedback as'througli connection yt9 of Figure 1, amplifier 2i. voltage adder 24, conductor 34 andfswitch S, and applied to voltage adder A8 'to `'alter the saw-tooth wave .in desired manner. Similarly, yifthe-loeam deviates inwardly, electrons rimpinge vupon target strip t, and the voltagedeveloped across resistor 50 Iis fed back as through connection `2! of V'.Eigure 1, amplifier 22, phase inverter 23, voltage adder 24, conductor 4341 and switch S, and .applied to voltage `adder 48. litwill be `observed that in the control of the spiral scanning arrangement ljust described, no switching means is required.

Thus far 'my description oi the invention lhas indicated fthat control strips are vprovided along `bothlengthwise --edges .of the path the control beam is intended to :fol-low thus providingfpos'itive control against unwanted deviationsineither `of two opposing directions.

eral scanning, the vertical deection signal, common to both the scanning and control beams, may be biased to such an extent that, in the absence of the correction signal, the control beam departs from its intended path by a predetermined amount in the direction of the control element associated therewith, and electrons which thereupon impinge upon the control strip are utilized to develop a correction voltage of sufficient magnitude to substantially overcome the bias. Hence, in the absence of voltage deviations, the control beam follows its intended path; and so, of course, does the controlled scanning beam.

The magnitude of the bias referred to above, may be substantially equal to the maximum defiection-voltage deviations, of opposite sign to the bias, which are anticipated. Such deviations, when they occur, merely tend to overcome, or at least diminish, the bias and thus cause the control beam to withdraw, at least partially, from the control strip, thereby diminishing the correction signal developed. The net result is that the beams remain substantially in their proper vertical positions.

When voltage deviations of the same sign as the bias occur, the control beam tends to invade the control strip by an increased amount and correction signals of increased magnitude are developed which are effective to overcome substantially the said voltage deviations of same sign.

Suitable switching and feedback means for the biased system above described are provided by switch l?, feedback path I9, amplier 2l, etc., of the circuit illustrated in Figure l, it being understood that only one switch and one feedback circuit are required for the biased system.`

Control means which does not employ a second electron beam to accomplish results similar to those of the instant invention are described and claimed in a joint copending application of mine and David E. Sunstein filed Nov. 23, 1946, Serial No. 711,968, and assigned to Philco Corporation. Certain advantages over the instant invention and also some disadvantages are obtained from the employment of a single beam as will become clear from a reading of the aforesaid joint cepending application.

I have described several embodiments of my invention. Other embodiments not requiring invention will occur to those skilled in the art.

Having described my invention,

I claim:

1. In an electrical system: means for producing a rst beam of electried particles; means for producing a second beam of electried particles; means, including common means, for simultaneously defiecting both said beams cyclical- 1y along similar preselected paths; means for maintaining said second beam at substantially flXed intensity during deection along said path; means associated with said second beam and responsive to deviations of said second beam from its preselected path for generating correcting voltages identifiable with the direction of said deviations; and means operating in synchronism vvith said deflection cycles for selectively apply- 1ng said correcting signals to both said beams in such manner as to oppose said deviations.

2. A cathode-ray system comprising: means for generating a first cathode-ray beam; means for generating a second cathode-ray beam; means, including common means, for eiecting simultaneous deflection of both said beams substantially along preselected paths; means for modulating the intensity of said first beam while maintaining the intensity of said second beam substantially xed during deflection along said paths; means responsive to deviations of said second beam from said preselected path for generating correcting voltages; and means responsive to said correcting voltages for so modifying the operation of certain of said common deecting means as to oppose said deviations.

3. In a cathode-ray system; means for generating a first cathode-ray beam; means for generating a second cathode-ray beam; means for applying signals from common sources to both said beams to deflect both said beams in predetermined similar manner; means for applying a modulating signal to said first beam only while maintaining said second beam at substantially Xed intensity; means associated with said second beam responsive to unwanted deviations of said second beam for generating correcting signals; and means responsive to said correcting signals and operative upon both said cathode-ray beams for opposing said deviations.

4. In a cathode-ray system; means for generating a cathode-ray scanning beam; means for generating a second cathode-ray beam for control purposes; means, including common sources of deflection-determining potentials, for dellecting said scanning beam substantially along a preselected scanning path and for simultaneously defiecting said control beam substantially along a preselected control path corresponding in pattern to said scanning path; means for maintaining said control beam at substantially xed intensity during deilection along said preselected control path; a first target plate so positioned as to be bombardedby electrons of said control beam in the event said beam departsin a predetermined direction from said preselected path; a second target plate so positioned as to be bombarded by electrons of said control beam in the event said beam departs in the opposite direction from said preselected path; means for deriving a first control voltage from the change in the electrical potential of said rst target plate resulting from bombardment thereof by said electrons; means for deriving a second control voltage from the change in the electrical potential of said second target plate resulting from the bombardment thereof by said electrons; and means for applying said first and second control voltages `in opposing relation to certain of said deflecting means to eiect control of both beams.

5. In a cathode-ray system: means for generating an electron scanning beam; means for generatinga second electron beam for control purposes; means, including common sources of deflection-'determining potentials, for deflecting said scanning beam cyclically in a preselected pattern comprised of a plurality of interlaced scanning elds and for simultaneously deecting said control beam cyclically in a preselected pattern comprised of a plurality of interlaced fields corresponding in conguration to said scanning nelds; means for maintaining said control beam at substantially fixed intensity during deflection in said preselected pattern; a plurality of interlaced groups of conductive control elements associated with said control beam; means responsive to changes in the electrical potential of said control elements for deriving signals from the bombardment of said control elements by said control beam; means synchronized with said deiiecting cycles for disregarding signals 4derived from the bombardment of control elements belonglng to a group corresponding to the eld then 13 intended to be scanned, and for utilizing signals derived from the bombardment of elements belonging to groups corresponding to elds not intended to be then scanned, to correct the deections of both said beams.

6. In a cathode-ray system: means for generating an electron scanning beam; means for generating a second electron beam for control purposes; means, including common sources of deflection-determining potentials, for simultaneously cyclically deflecting both said beams in accordance With preselected patterns; means for maintaining said control beam at substantially iiXed intensity during said deflection; a rst group of conductive control elements positioned to be bombarded by electrons of said control beam in the event said `control beam departs in a first direction from a first portion of said pattern and in a second direction from a second portion of said pattern; a second group of conductive control elements positioned to be bombarded by electrons of said control beam in the event said control beam departs in a second direction from a iirst portion of said pattern and in a first direction from a second portion of said pattern; means responsive to changes in the electrical potential of said control elements for deriving control voltages from the bombardment of said control elements; and means synchronized with said deflection cycles for utilizing said control voltages to oppose departures of both said beams from their respective preselected patterns.

7. In an electrical system: means for generating a rst beam of electrified particles; means for generating a second beam of electried par- 3 ticles; means for applying potentials from common sources to both beams to place both beams substantially in predetermined similar conditions; means for applying an additional signal to said rst beam to vary its intensity while maintaining said second beam at substantially xed intensity; means associated With said second beam responsive to unwanted deviations of said second beam from said predetermined condition for generating correcting signals characteristic of the nature of said deviations; and means responsive to said correcting signals and operative upon both said cathode-ray beams for opposing said deviations.

8. A cathode-ray system comprising: means for generating a rst cathode-ray beam; means for generating a second cathode-ray beam; means, including common means, for effecting concurrent deflection of both said beams substantially along preselected paths; means for maintaining said second beam at substantially iiXed intensity during deflection along said path; means associated With said second beam responsive to changes in the electrical potential of said path for detecting deviation of said second beam from said preselected path and for generating control signals characteristic of the nature of said deviation; and means responsive to said control signals and operative upon both said cathode-ray beams for opposing said deviation.

ALLEN C. MNSTER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,210,078 Headrick Aug. 6, 1940 2,415,059 Zworykin Jan. 28, 1947 

